The operation of a plasma processing apparatus, and similar devices in connection with the fabrication of semiconductor substrates or flat panel displays of various types are well known. In this regard, such assemblies include a chamber housing a pair of essentially planar electrodes that are spaced in substantially parallel relation to define a reaction space therebetween. On a first of the electrodes is positioned a semiconductor wafer to be processed. For such processing to occur, an appropriate gaseous medium is introduced into the chamber, and then one or more suitable high radio frequency voltages are applied across the pair of electrodes to generate an electrical discharge which forms a plasma therebetween the electrodes. This plasma etches or otherwise suitably processes the semiconductor wafer in an appropriate fashion.
Such chambers, of course, may be used to etch material previously deposited on the semiconductor wafer, or may be employed to deposit materials onto the same semiconductor wafer. In these previous prior art assemblies, and more specifically in capacitive plasma reactors, the radio frequency power may be supplied to one or both of the electrodes, and any capacitive discharge takes place between these parallel electrodes. It has been well known that it is important, from an efficiency, and uniformity standpoint, to confine the resulting plasma essentially to the interaction space between the two electrodes. It is understood, however, that some plasma may permeate or move throughout the whole processing chamber. If this occurs, erosion or deposition may take place in these remote regions causing a resulting particle contamination in the reaction chamber thus lowering the performance and yield rates that can be produced from the same reaction chamber. Still further, this deposition and erosion may shorten the lifespan of the reaction chamber or its components. In addition to the foregoing, if plasma is not confined within the processing region charged particles produced by the plasma may collide with unprotected regions of the reaction chamber causing further impurities, particulate matter, and contamination to be generated and which may result in the contamination of the surface of any semiconductor substrates which are being processed in the chamber.
The prior art is replete with numerous examples of devices, and methodology which have attempted to solve the difficulties associated with plasma confinement. For example, U.S. Pat. No. 6,562,189, the teachings of which are incorporated by reference herein, discloses a plasma chamber which employs a plasma-confining magnet assembly to inhibit the diffusion of the plasma. While this arrangement has operated with some degree of success, its principal shortcoming is that if the magnetic field of the magnet is too strong, it may potentially damage electrically sensitive components which are located on a semiconductor substrate that is being processed. Obviously, if the magnet employed with such an assembly is too weak, the plasma diffusion cannot be effectively confined, and the resulting contamination, noted above, results. In addition to the foregoing, U.S. Pat. No. 5,534,751 discloses a plasma etching apparatus, including a stack of quartz rings which are spaced apart to form slots therebetween, and when are positioned so as to surround an interaction or reaction space between the two electrodes of the apparatus. In the arrangement as disclosed, and when charged particles such as ions or electrons pass through the narrow gaps defined by the quartz ring, many of the charged particles will collide with the surface of the quartz ring thus substantially confining the plasma diffusion. However, the principal shortcoming in this device is that this arrangement cannot completely prevent charged particles from leaking outside the processing region nor can it completely prevent the leakage of electromagnetic waves or prevent a secondary radio frequency discharge of the leaked charged particles outside the processing region. Consequently, contamination can still be generated.
In addition to the foregoing, U.S. Pat. No. 5,998,932 relates to a focus ring arrangement for substantially eliminating unconfined plasma in a plasma processing chamber, and which uses grounded conducting extensions to substantially reduce the density of eqipotential lines outside the processing region. This apparatus, in principal, is supposed to reduce the collision of leaked charged particles with the wall of the reaction chamber outside of the processing region so as to prohibit the generation of unwanted plasma. This unwanted plasma is caused by the electric field outside the processing region. In practice, however, this method has shown that it cannot completely prevent the formation of an electric field outside the processing region.
Still further, in U.S. Pat. No. 6,178,919, a perforated plasma confinement ring, and a plasma reactor is disclosed, and which includes a sealing ring made of a conducting material which includes apertures or holes that permit a reaction gas to escape from the processing region. This conductive sealing ring is grounded, and absorbs electrons in the exhaust reaction gas thus neutralizing the charge, and thereby reduces the number of electrons in the plasma, and further increases the density of ions within the processing region. While this device works with some degree of success it should be understood that the collision of ions of the plasma onto the surface of the conductive sealing ring may cause contamination to be generated in the chamber, and other electrical discharges.
From a detailed study of the prior art patents noted, above, it will be seen that principally two existing methods are used in the industry to confine plasma. A first method is to confine the plasma with an insulating sealing ring that physically blocks the plasma exhaust gas. Further, a second method is to confine the plasma by adjusting the resulting electrical field.
A plasma confinement apparatus, and method for confining a plasma which avoids the shortcomings attendant with the prior art devices and practices, and methodology which have been utilized heretofore is the subject matter of the present application.